Certain materials, such as carbon fiber reinforced plastic (“CFRP”) materials, may be prone to damage from electrical discharges, such as lightning strikes. Therefore, those skilled in the art continue to seek techniques for reducing or eliminating damage to materials due to electrical discharges.
For example, various spectrally selective coatings and methods for minimizing the effects of electrical discharges, such as lightning, are disclosed in U.S. Ser. No. 12/474,965 filed on May 29, 2009, the entire contents of which are incorporated herein by reference. However, the design of coatings and materials capable of resisting electrical discharges may require, or may be improved by, knowing the spectral energy and associated blackbody temperature of the electrical discharge.
Currently, the blackbody temperature of a lightning strike may be assumed from published values. Unfortunately, the published values of lighting strike temperatures are far ranging in values from approximately 8,000° K to 25,000° K.
Blackbody temperatures may also be estimated based upon post lightning strike thermal analysis and the radiative temperatures required to cause similar damage levels. However, calculating the required blackbody temperature to duplicate lighting strike test damage to CFRP panels is an inaccurate and indirect way of determining the lighting plasma blackbody temperature, and requires accurate knowledge of material layer thermophysical properties during and after extreme erosion.
Photographic techniques are currently used to determine the presence and amount of electrical sparking. However, film and digital photographic techniques do not provide a measure of electrical discharge energy levels and, therefore, cannot be used to determine blackbody temperature.
Other measurement techniques involve the use of spectral radiometers to measure the spectral energy from an electrical discharge. A spectral radiometer may be used to measure the relative spectral energy levels associated with an electrical discharge, but spectral radiometers do not provide the blackbody temperature of the electrical discharge.
A spectral radiometer may also be used to measure absorption lines. The absorption lines occur as a result of atmospheric constituents interacting with the electrical discharge plasma. The characteristic measurement results in a curve showing energy versus wavelength with many narrow lines which rise above the nominal curve height. The width of these lines may be used to analytically provide equivalent blackbody temperature values. This method is highly indirect, requiring many assumptions, in part because the absorption lines are broader at the base than at the peak, and is not based upon accurate measurements of the physical quantities in question because the emission lines coincide with absorption lines. The emissions are also very readily absorbed and, therefore, not present at the sensor aperture in relation to the physical temperature of the arc source.
Accordingly, those skilled in the art continue to seek techniques for determining the blackbody temperature of an electrical discharge.